Fixing device and image forming apparatus

Abstract

A fixing device which fixes a toner image borne on a recording medium includes a rotatable fixing roll member, a rotatable tension roll member, a rotating fixing belt member stretched between the fixing roll member and the tension roll member, a heater which heats the fixing belt member, a pressing member which presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip part, and a belt moving direction changing member which is interposed between the fixing belt member and the fixing roll member on a downstream side of the nip part, and changes a moving direction of the fixing belt member. Width “Wbe” of the fixing belt member, width “Wpr” of the pressing member, and width “Wpe” of the belt moving direction changing member are set to satisfy the following relation: Wpr≦Wbe<Wpe.

1 . A fixing device which fixes a toner image borne on a recording medium, comprising: 
 a rotatable fixing roll member;    a rotatable tension roll member;    a rotating fixing belt member stretched between the fixing roll member and the tension roll member;    a heater which heats the fixing belt member;    a pressing member which presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip part; and    a belt moving direction changing member which is interposed between the fixing belt member and the fixing roll member on a downstream side of the nip part, and changes a moving direction of the fixing belt member,    wherein width “Wbe” of the fixing belt member, width “Wpr” of the pressing member, and width “Wpe” of the belt moving direction changing member are set to satisfy the following relation:      Wpr≦Wbe<Wpe.    
   
   
       2 . The fixing device according to  claim 1 , 
 wherein the pressing member is a pressing roll member having an elastic layer on its surface.    
   
   
       3 . The fixing device according to  claim 1 , further comprising: 
 a walk section which causes the fixing belt member to walk,    wherein a walk rate “Bw” of the fixing belt member by the walk section is set to satisfy the following relation;        Bw <( Wpe−Wpr )/2.    
   
   
       4 . The fixing device according to  claim 1 , 
 wherein width “Lhr” of the fixing roll member is set to satisfy the following relation:      Wbe<Lhr≦Wpe.    
   
   
       5 . A fixing device which fixes a toner image borne on a recording medium, comprising: 
 a rotatable fixing roll member;    a rotatable tension roll member;    a rotating fixing belt member stretched between the fixing roll member and the tension roll member;    a pressing roll member which presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip part, the pressing roll member having an elastic layer on its surface; and    a bending member formed of metal which is interposed between the fixing belt member and the fixing roll member on a downstream side of the nip part, and bends the fixing belt member at a greater curvature,    wherein the bending member and the pressing roll member are not directly contacted owing to the belt member interposed between the bending member and the pressing roll member, even when the fixing belt member walks.    
   
   
       6 . The fixing device according to  claim 5 , 
 wherein a side edge of the fixing belt member does not protrude out of a side edge of the bending member, even when the fixing belt member walks.    
   
   
       7 . An image forming apparatus, comprising: 
 a toner image forming section which forms a toner image;    a transfer section which transfers the toner image formed by the toner image forming section onto a recording medium; and    a fixing device which fixes the toner image transferred onto the recording medium on the recording medium,    wherein the fixing device includes:    a rotatable fixing roll member;    a rotatable tension roll member having a thermal heater;    a rotating fixing belt member stretched between the fixing roll member and the tension roll member;    a pressing roll member which presses a portion of the fixing roll member around which the fixing belt member is wound to form a nip part, the pressing roll member having an elastic layer on its surface; and    a peeling member which is interposed between the fixing belt member and the fixing roll member on a downstream side of the nip part, and peels the recording medium from the fixing belt member,    wherein width “Wbe” of the fixing belt member, width “Wpr” of the pressing roll member, and width “Wpe” of the peeling member are set to satisfy the following relation:      Wpr≦Wbe<Wpe.    
   
   
       8 . The image forming apparatus according to  claim 7 , further comprising: 
 a walk section which causes the fixing belt member to walk,    wherein a walk rate “Bw” of the fixing belt member by the walk section is set to satisfy the following relation:        Bw <( Wpe−Wpr )/2.    
   
   
       9 . The image forming apparatus according to  claim 7 , 
 wherein width “Lhr” of the fixing roll member is set to satisfy the following relation:      Wbe<Lhr≦Wpe.    
   
   
       10 . A fixing device which fixes a toner image borne on a recording medium, comprising: 
 a rotational member;    an endless belt member which is wound around the rotational member and rotates along with a rotation of the rotational member;    a pressing member which presses the rotational member and the belt member wound around the rotational member to form a nip part; and    a belt moving direction changing member which is interposed between the belt member and the rotational member on a downstream side of the nip part, and changes a moving direction of the belt member,    wherein width “Wbe” of the belt member, width “Wpr” of the pressing member, and width “Wpe” of the belt moving direction changing member are set to satisfy the following relation:      Wpr≦Wbe<Wpe.